A now thoroughly discredited attempt to discredit climate science, in which illegally obtained emails of scientists at the UK's climate research center at the University of East Anglia were carefully cherry-picked for out-of-context words and phrases that could be manipulatively interpreted as damning, and distributed to the media through, among other methods, fossil-fuel industry funded denialist organizations.
The scientists involved had no difficulty explaining the contexts behind the cherry-picked words and terms, and all were exonerated by subsequent investigations. Unfortunately, however, many more-casual observers who only followed the media frenzy resulting from the release of the emails remain unaware of the resolution of the matter, and still naively believe that Climategate "proved" malfeasance among climatologists.
The hackers who stole the emails from the University of East Anglia's servers have never been identified.
Sarah Palin: Climategate proves that all of climate science is a fraud!
Michael Mann: Sarah, you're so full of shit your eyes must be brown.